[PATCH v2] coresight: etm4x: Fix crash observed on Qcom ETM parts with 'Low power override'

[Bhupesh Sharma]

Some Qualcomm ETM implementations require skipping powering up
the trace unit, as the ETMs are in the same power domain as
their CPU cores.

Via commit 5214b563588e ("coresight: etm4x: Add support for
sysreg only devices"), the setting of 'skip_power_up' flag was
moved after the 'etm4_init_arch_data' function is called, whereas
the flag value is itself used inside the function. This causes
a crash when ETM mode 'Low-power state behavior override' is set
on some Qualcomm parts.

Fix the same.

Fixes: 5214b563588e ("coresight: etm4x: Add support for sysreg only devices")
Cc: Mike Leach <mike.leach at linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
Cc: Mathieu Poirier <mathieu.poirier at linaro.org>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma at linaro.org>
---
 - v1 can be seen here: https://lore.kernel.org/lkml/20220803191236.3037591-1-bhupesh.sharma@linaro.org/
 - Addressed the review comments from Suzuki.
 - Rebased on linux-next.

 drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index d39660a3e50c..14c1c7869795 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -977,6 +977,16 @@ static bool etm4_init_sysreg_access(struct etmv4_drvdata *drvdata,
 	if (!cpu_supports_sysreg_trace())
 		return false;
 
+	/*
+	 * Some Qualcomm implementations require skipping powering up the trace unit,
+	 * as the ETMs are in the same power domain as their CPU cores.
+	 *
+	 * Since the 'skip_power_up' flag is used inside 'etm4_init_arch_data' function,
+	 * initialize it before the function is called.
+	 */
+	if (fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
+		drvdata->skip_power_up = true;
+
 	/*
 	 * ETMs implementing sysreg access must implement TRCDEVARCH.
 	 */
@@ -1951,8 +1961,7 @@ static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
 		return -EINVAL;
 
 	/* TRCPDCR is not accessible with system instructions. */
-	if (!desc.access.io_mem ||
-	    fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
+	if (!desc.access.io_mem)
 		drvdata->skip_power_up = true;
 
 	major = ETM_ARCH_MAJOR_VERSION(drvdata->arch);
-- 
2.35.3